Isopropyl alcohol produced from a plant-derived material can be converted to propylene through dehydration, so that it is promising as a carbon-neutral raw material for propylene. Since all the developed countries are currently required by Kyoto Protocol to reduce their amounts of carbon dioxide emissions by 5% based on those in 1990, carbon-neutral propylene is extremely important due to its versatility in view of the global environment.
Bacteria that utilize plant-derived materials to produce isopropyl alcohol (e.g., see Chinese Patent Application Publication No. CN 1043956 A and Japanese Patent Application laid-Open (JP-A) No. 61-67493) already exist in nature. However, they are known to have low productivity of isopropyl alcohol and to generate alcohols such as butanol and ethanol as by-products. Since the azeotropic temperatures of butanol and ethanol are close to that of water, it is difficult to separate isopropyl alcohol from butanol and/or ethanol by easy methods such as simple distillation. Therefore, it is thought that collection of isopropyl alcohol from fermentation broth in which butanol and/or ethanol coexist(s) with isopropyl alcohol requires distillation using incidental facilities such as a rectifying column, so that the purification process is expected to be complicated.
CN 1043956 A describes a method for producing butanol, ethanol, acetone and isopropanol in which Clostridium Butanoiacetonicus G.V is cultured in a culture medium, which has been supplemented with maize and molasses, and subjecting the thus-obtained culture to distillation redistillation and fractional distillation. However, in Examples described in the literature, yields of butanol, ethanol, acetone and isopropanol in the culture medium are not described at all, and the amount of each of these components which should have been finally obtained by the fractional distillation is not described. Thus, the actual production of isopropanol, butanol, ethanol and acetone cannot be seen from the literature.
JP-A 61-67493 describes that the culture medium obtained by culturing a bacterium of the genus Clostridium contains butanol, the amount of which is larger than that of isopropyl alcohol, and small amounts of ethanol and acetone. This literature describes that a common method of separation and purification to obtain isopropyl alcohol from the obtained culture medium is a method in which the culture medium is filtered, distilled several times, concentrated and subjected to separation by salting out to obtain an oil content, which is subsequently subjected to fractional distillation by an apparatus having a fractionating column.
On the other hand, it has been known that acetone can be produced by introducing, to E. coli, genes of acetoacetate decarboxylase, CoA transferase and thiolase which are derived from a bacterium of the genus Clostridium (Clostridium Acetobutylicum) and culturing the obtained recombinant E. coli (e.g., Lourdes L Bermejo et al.: Applied and Environmental Microbiology, Vol. 64, N0.3, p. 1079-1085, (1998)).